The present invention relates to isobutylene rubber particles, isobutylene rubber-containing graft copolymer particles and a resin composition. More particularly the present invention relates to isobutylene rubber particles and isobutylene-based graft copolymer particles, which are useful as an impact resistant resin or an impact modifier having excellent weatherability and heat stability, and further to a thermoplastic resin composition containing these particles which exhibits a high impact resistance with maintaining properties such as weatherability and thermal stability and is suitable for production of molded articles such as sheet and film.
Impact modifiers have been used for imparting an impact resistance to various resins. Various impact modifiers have been proposed, and a core-shell graft copolymer prepared by graft-polymerizing a vinyl monomer (which forms a shell layer) onto a rubber-containing crosslinked particles (which forms a core layer) has been industrially widely used as an impact modifier. It has been recognized that the rubber component of the core layer serves to improve the impact resistance of thermoplastic resins, and the vinyl polymer of the shell layer serves to have a compatibility (namely dispersibility and adhesion property) with various resins. For example, as an impact modifier is well known a graft copolymer of a polybutadiene rubber and a vinyl monomer graft-polymerized onto the rubber. However, since a polybutadiene rubber contains unsaturated bonds and accordingly is thermally unstable, such an impact modifier having excellent thermal stability and weatherability has not been obtained.
A graft copolymer prepared by graft-polymerizing a vinyl monomer onto an acrylic rubber is also known as an impact modifier. An acrylic rubber is excellent in thermal stability and weatherability, but it has a relatively high Tg (glass transition temperature) and therefore the graft copolymer does not have a significant effect of improving impact resistance.
An impact modifier having a low Tg and being excellent in thermal stability and weatherability is known from JP-A-60-252613 and JP-A-2-8209, which disclose a graft copolymer prepared by graft-polymerizing a vinyl monomer onto a polyorganosiloxane rubber (silicone rubber). This impact modifier has, to some degree, the effect of improving impact resistance, but more improvement has been demanded. Also, this impact modifier deteriorates the processability and surface gloss of thermoplastic resins incorporated therewith.
Accordingly, an object of the present invention is to provide an impact modifier which is superior in weatherability and thermal stability and can improve the impact resistance of various thermoplastic resins without substantially lowering the processability and surface gloss.
A further object of the present invention is to provide rubber particles or rubber-containing graft copolymer particles which are useful as such an impact modifier.
Another object of the present invention is to provide a thermoplastic resin composition which is remarkably improved in impact resistance without substantially lowering the properties that the thermoplastic resins originally possess, such as excellent weatherability, heat stability and processability.
These and other objects of the present invention will become apparent from the description hereinafter.